Investigators said Friday they are trying to figure out how two chimpanzees that viciously attacked a visitor at an animal sanctuary escaped from their cages.

The chimps chewed off St. James Davis' nose and severely mauled his genitals and limbs Thursday before the son-in-law of the sanctuary's owner shot the animals to death, authorities said.

According to this account and two others in Newsday and a New Zealand newspaper , Mr. Davis and his wife were throwing a birthday party for their adopted Chimpanzee, Moe, when apparently the other two apes became jealous (!) and attacked. From Newsday:

St. James Davis 62, took the brunt of the attack, the ferocity of which left paramedics stunned.

"I had no idea a chimpanzee was capable of doing that to a human," said Kern County Fire Capt. Curt Merrell, who was among the first on the scene.